Cu—Cr—O composite materials are usually prepared by a variety of synthetic methods, involving the reduction of Cu—Cr oxide prepared by Adkins' route, template method, citric acid complex method, precipitation and thermal decomposition, conventional high temperature method, coprecipitation method, gel method, hydrothermal method, microemulsion method, heterogeneous precipitation method, sonochemical method, combustion method, sol-gel method. These methods allow substantial reduction of the temperature of precessing, minimizing therefore the undesired aggregation of the particles during calcinations. Among these methods, the sol-gel process shows promising potential for the synthesis of mixed oxides, owing to its high purity, good chemical homogeneity, low calcinations temperature, etc. The major disadvantages of using the metal alkoxides based sol-gel process are its moisture sensitivity and the unavailability of suitable commercial precursors especially for mixed-metal oxides. The sol-gel synthesis of mixed metal oxides from alkoxide mixture usually suffers from the different hydrolysis susceptibilities of the individual components and the benefits of improved homogeneity can be lost during the hydrolysis of the alkoxides, which may ultimately lead to component segregation and mixed phases in the final materials. Non-alkoxide sol-gel process, involving hydrolysis and condensation of metal salts, avoids the disadvantages of alkoxide sol-gel process, however has still the disadvantage of different hydrolysis susceptibilities of the individual components.
These preparation methods are not good enough largely because many of their metal alkoxides are expensive, and still others are sensitive to moisture, heat, and light making their use and long-term storage difficult. In addition, some metal alkoxide are not commercially available or are difficult to obtain, thus precluding detailed studies on the preparation and application. The main advantage of our process that no alkoxide is used in this process and the preparation method is highly reproducible. The yield is also very high and it is as much as 95%. To the best of our knowledge there is no report for the preparation of Cu—Cr oxide using hydrazine and cetyltrimethylammonium bromide.
Reference may be made to the article J. Am. Chem. Soc. 54 (1932) 1138 by Adkins et al where they decomposed copper ammonia chromate precipitation to prepare Cu—Cr oxide. Reference may also be made to the article Chem. of Materials 17 (2005) 1919 where A. B. Futertes et al used silica xerogel as the template to synthesize the CuCr2O4 spinels. Reference may also be made to the article Appl. Catal A: 279 (2005) 59 by Tanaka et al where they used citric acid complex method to synthesize Cu—Cr oxide materials. Reference may also be made to the articles Solid State Sci. 9 (2007) 750 where Cheng et al has used the precipitation method to prepare Cu—Cr oxide materials. Reference may also be made to the articles Thermochim Acta 254 (1995) 235 where Nair et al used thermal decomposition method to stnthesize Cu—Cr oxide. Reference may also be made to the articles J. Mater. Chem. 20 (2010) 755 by Liang et al where they used non-alkoxide sol-gel route to prepare Cu—Cr oxide materials. Cu—Cr oxide have been used as catalyst for the chemical reactions of hydrogenation, dehydrogenation, alkylation, oxidation, in car exhaust purification. Although, there are only few reports for the oxidation over Cu—Cr oxide catalysts, but to the best of our knowledge there is no report where a single catalyst is used for the selective oxidation of benzene, toluene and ethylbenzene with very good selectivity.
Reference may also be made to the articles Reac. Kinec. Catal. Lett. 94 (2008) 345 by Ionescu et al where they used Cu—Cr oxide catalyst was used for the total oxidation of benzene to get CO2. Reference may also be made to the articles Appl. Catal. B-Environmental 19 (1998) 37 by Vekinis Vekinis et al where Cu—Cr oxide was used for the oxidation of carbon monoxide.
Thus, although there are some reports for the selective oxidation of benzene, toluene and ethylbenzene using different heterogeneous catalysts, but there is no reports where Cu—Cr oxide was used for these oxidation reactions. Additionally the catalyst used have a limited activity under operating condition, so improvement of the catalysts is necessary for industrial application.